Production of eutectic bodies by unidirectional solidification

ABSTRACT

Eutectic bodies with controlled morphology are produced by establishing a thin liquid film of a eutectic composition on a hot supporting surface, growing a body of said composition from said film by unidirectional solidification, pulling the body away from the film at a rate consistent with the rate of solidification, and replenishing the film so as to sustain continuous growth.

United States Patent Mlavsky Apr. 2, 1974 1 PRODUCTION OF EUTECTICBODIES BY 3,434,892 3/1969 Heimke 148/].6 x UNIDRECTIONAL SOLIDIFICATION3,591,348 7/1971 La Belle 23/301 SP 3,694,193 9/1972 Carpay et al.75/129 [75] Inventor: Abraham 1. Mlavsky, Lincoln, Mass.

[73] Assignee: Tyco Laboratories, Inc., Waltham, Primary EXami"erHYlandBizot Mass Assistant Examiner-E. L. Weise Attorney, Agent, orFirmSchiller & Pandiscio 22 F1led: Nov. 8, 1971 [21] Appl. No.: 196,448[57] ABSTRACT Eutectic bodies with controlled morphology are pro- [52]U5. Cl 75/135, 23/301 SP duccd y hing a hin liq i film f a eu ec ic [51]Int. Cl. C22c 1/02 composition on a hot pp g surface, g g a [58] Fieldof Search 75/135; 23/301 SP; body of said composition from said film byunidirec- 148/1,6 tional solidification, pulling the body away from thefilm at a rate consistent with the rate of solidification, [56] Referene Cited and replenishing the film so as to sustain continuous UNITEDSTATES PATENTS growth- 3,124,452 3/1964 Kraft 75 135 13 Claims, 6Drawing Figures l6 57 ER Il 8 I 8 X N PATENTEDAPR 21914" 31801309,

SHEET 2 UF 2 F G 0 6 INVENTQR ABRAHAM I. MLAVSKY BY 9 pana iuib AT TORNE YS PRODUCTION OF EUTECTIC BODIES BY UNIDIRECTIONAL SOLIDIFICATION Thisinvention relates to production of eutectic materials and moreparticularly to production of eutectic compositions by controlleddirectional solidification.

It is recognized in the art that unidirectional solidification ofvarious eutectic compositions may have the effect of providing productshaving unique crystallographic and mechanical properties. In thisconnection see F. D. Lamkey et al., The Microstructure, Crystallography,and Mechanical Behavior of Unidirectionally Solidified Al-Al NiEutectic, Transactions of the Met allurgical Society of AIME, Vol. 233,pp. 334-341, Feb., 1965; and R. W. I-Iertzberg et al., MechanicalBehavior of Lamella (Al-CuAl and Whisker Type (Al-Al Ni)Unidirectionally Solidified Eutectic A]- loys", Transactions of theMetallurigcal Society of AIME, Vol 233, pp. 342-354, Feb., 1965. It hasbeen demonstrated that if l) a planar liquid-solid interface isestablished in a binary eutectic alloy by proper control of heat flowduring the solidification process and (2) the interface is movedunidirectionally, it is possible to produce a eutectic crystal structureconsisting of an essentially parallel array of discrete phases. Thus ithas been possible to produce two dominant phase microstructures: (a) onecomprising parallel alternating rods of one phase embedded in acontinuous matrix of the second phase. The directional solidificationtechnique usually used for this purpose essentially consists of meltinga mixture of the refined constituents of the desired eutectic,maintaining the melt long enough to insure complete mixing, and coolingthe melt to form ingots. Then these ingots are remelted in a crucibleand unidirectionally solidified by unidirectionally withdrawing thecrucible from the heat source (or vice versa) at as uniform a rate aspossible with the object of producing a constant rate of growth andmaintaining a constant thermal gradient in the liquid ahead of theliquid-solid interface.

While this prior art technique has produced eutectic materials havingunique properties, e.g. an alloy of highly anisotropic mechanicalproperties comprising single crystal whiskers of Al Ni in an aluminummetal matrix, it has a number of limitations. For one thing, the centerof the melt tends to cool at a slower rate (particularly in a largediameter crucible) and hence the crystallographic structure tends tovary along planes parallel to the liquid-solid interface. A furtherlimitation is the inability to grow such eutectic compositions inindefinite lengths. Further problems are phase discontinuities anddifficulty in (a) maintaining a planar liquid-solid interface, (b)controlling the temperature gradient at that interface within closelimits, and (c) holding the rate of growth constant.

Accordingly, the primary object of this invention is to provide a newand improved method of unidirectionally solidifying eutecticcompositions so as to produce bodies that are characterized by uniquecrystallographic relationships between the constituent phases thereof.

Another important object of this invention is to provide a method ofproducing binary eutectic compositions as duplex single crystals.

Still another important object is to provide a method of producingbinary eutectic compositions having microstructures that consist ofsubstantially parallel alternating lamellae of each phase or long thinparallel rods of one phase embedded in a continuous matrix of the otherphase.

A further object is to provide eutectic compositions having uniquemicrostructures.

The foregoing objects are achieved by establishing a relatively thinmolten film of the eutectic composition and growing and pulling acrystalline body from the thin film while simultaneously replenishingthe film by feeding thereto additional melt under the influence ofsurface tension. The process may be conducted on a continuous basis soas to produce bodies of indefinite length and the body may be grown to apredetermined arbitrary cross-sectional configuration. v

Other features and advantages of the process and the nature of theproducts produced thereby are set forth in or rendered obvious by thefollowing detailed description of the invention which is to beconsidered together with the accompanying drawings wherein:

FIG. 1 is a vertical sectional view of one form of crucible and diearrangement for practicing the invention;

FIG. 2 is a fragmentary view of the apparatus of FIG. 1 showing a filmof melt and a seed for effecting solidification and growth of a eutecticbody;

FIG. 3 is a vertical sectional view of a second crucible and diearrangement;

FIG. 4 is a view similar to FIG. 1 showing a die assem bly for growing ahollow eutectic body;

FIG. 5 is a photomicrograph of a transverse section of a eutectic bodycomprising UP and NaCl grown according to this invention; and

FIG. 6 is a photomicrograph of a transverse section of a eutectic bodycomprising LiF and CaF grown according to this invention.

The present inventions utilizes the so-called EFG process previouslyknown for growing monocrystalline bodies of materials such as alumina.The term EFG stand for edge-defined, filmfed growth and designates aprocess for growing crystalline bodies from a melt. The essentialfeatures of the EFG process are described in US. Pat. No. 3,591,348,issued July 6, 1971 to Harold E. LaBelle, Jr. for METHOD OF GROWINGCRYSTALLINE MATERIALS.

In the EFG process the shape of the crystalline body that is produced isdetermined by the external or edge configuration of a horizontal endsurface of a forming member which for want of a better name is called adie, although it does not function in the same manner as a die. By thisprocess a variety of complex shapes can be produced commencing with thesimplest of seed geometries, namely, a round small diameter seedcrystal. The process involves growth on a seed from a liquid film orfilm material sandwiched between the growing body and the end surface ofthe die, with the liquid in the film being continuously replenished froma suitable reservoir of melt via one or more capillaries in the diemember. By appropriately controlling the pulling speed of the growingbody and the temperature of the liquid film, the film can be made tospread (under the influence of the surface tension at its periphery)across the full expanse of the end surface of the die until it reachesthe perimeter or perimeters thereof formed by intersection of thatsurface with the side surface or surfaces of the die. The angle ofintersection of the aforesaid surfaces of the die is such relative tothe contact angle of the liquid film that the liquid s surface tensionwill prevent it from overrunning the edge or edges of the dies endsurface. Preferably the angle of intersection is a right angle which issimplest to achieve and thus most practical to have. The growing bodygrows to the shape of the film which conforms to the edge configurationof the dies end surface. Thus it is possible to grow a substantiallymonocrystalline body with any one of a variety of predeterminedcross-sectional configurations, e.g. bodies with circular, square orrectangular crosssection. Furthermore, since the liquid film has no wayof discriminating between an outside or inside edge of the dies endsurface, it is possible to grow a monocrystalline body with a continuoushole by providing in that end surface a blind hole, i.e. a cavity of thesame shape as the hole desired in the growing body, provided, however,that any such blind hole is made large enough so that surface tensionwill not cause melt film around the hole to fill in over the hole. Fromthe foregoing brief description it is believed clear that the termedgedefined, film-fed growth denotes the essential feature of the EFGprocess the shape of the growing crystalline body is defined by the edgeconfiguration of the die and growth takes place from a film of liquidwhich is constantly replenished.

It has been determined that essential factors contributing to theessential monocrystalline character of the bodies that are grown by theEFG process are the relatively shallow depth of the melt film supportedby the die, the fact that the film-supporting surface of the diefunctions as a substantially isothermal heater (i.e. the film-supportingsurface has a substantially flat temperature profile along its entireexpanse), and the fact that melt film is not affected by perturbationsin the melt reservoir and can be maintained at an average temperaturelower than the average temperature of the melt in the reservoir. Thethin melt film has a sharp vertical temperature gradient and arelatively small horizontal temperature gradient. It has been found thatbecause of these factors, coupled with the additional fact that thethickness, i.e. depth, of the melt film can be maintained substantiallyconstant by adjusting the rate of heating and the pulling speed, it ispossible to utilize the EFG technique to unidirectionally solidifyeutectic compositions so as to produce coherent eutectic bodies ofindefinite length and controlled cross-sectional configurations. As usedherein, the term coherent eutectic denotes a eutectic composition havinga high order of regularity of dispersal of one phase in another.Eutectic compositions produced in accordance with this invention arecharacterized by crystallographic properties that are substantially moreuniform than eutectic bodies of the same chemical composition producedby prior art unidirectional solidification techniques. Depending upontheir chemical constituents, eutectic compositions produced as hereindescribed may be used, for example, as structural materials for jetengines and to produce components for electrical and electronic devicesand systems.

THe present invention may be used to unidirectionally solidify a widevariety of eutectic compositions, including, for example, Al-Al Ni,Al-CuAl Pb-Sn, Zn- Sn, Cd-Zn, Mg-Mg Al NiSb-lnSb, and Cu-Cr eutecticalloys, nickel-base super alloys (such as those commercially designatedas PWA Nos. 101 1A, 655, 659 and 689), LiF-NaCl, and LiF-CaF Althoughthe following detailed description of the invention includes specificexamples of producing bodies of only a few of the foregoing eutecticcompositions, persons skilled in the art will appreciate that theinvention is applicable to directionally solidifying all of theforegoing corn positions and also many other compositions, including,but

not limited to, those specified by G. A. Chadwick, Eu-

tectic Alloy solidification Progress In Materials Science, Vol. 12, No.2, Pergamon Press, Oxford, 1963.

In the following description like reference characters on the drawingsrefer to like elements in the several figures.

Turning now to FIG. 1, the illustrated apparatus comprises a crucible 2for holding a reservoir supply of a melt 4 of a eutectic compositionwhich is to be directionally solidified in accordance with thisinvention. The crucible is made of a material that will withstand theoperating temperatures and will not react with the die assemblyhereinafter described and will not react with or dissolve in the melt 4.The crucible is mounted within a susceptor 6 by means of a plurality ofshort rods 8. The susceptor is made of a material that will not evolvesubstances that will react with the crucible and preferably is spacedfrom the crucible if it is madeof a material that will react with thecrucible or die assembly at the operating temperatures. The top end ofthe susceptor is open but its bottom end is closed off by an end wall10.

Mounted within the crucible is a die assembly 14 that comprises a disc16 that is locked to the crucible by a removable collar 17. The disc 16functions as a heat shield to reduce radiative heat loss from the meltand also supports a die member in the form of a cylindrical,vertically-extending solid non-porous rod 18 which is securedly mountedwithin a centrally located hole in the disc. Rod 18 extends a shortdistance above the disc and its bottom end terminates short of thebottom of the crucible. Rod 18 has a flat, substantially horizontal topend surface 20 and several through holes in the form ofaxially-extending bores 22 that are uniformly spaced about the axis ofthe rod and are sized to function as capillaries for the melt 4. Disc 16and rod 18 are made of a material that will not react with the crucibleand will not react or dissolve in the melt. Additionally, the rod 18 ismade of a material that is wetted by the melt and the diameters ofcapillaries 22 are such as to cause melt to rise up and fully fill themso long as the bottom end of the rod is trapped by, i.e. submersed in,the melt.

The apparatus of FIG. 2 is mounted in a suitable induction heatingfurnace (not shown) that is adapted to envelope the crucible and thegrowing eutectic body in an inert atmosphere and includes a pullingmechanism that is adapted to position a seed crystal as hereinafterdescribed and to pull the seed at a controlled rate as melt solidifieson the seed. One form of furnace that may be used in the practice ofthis invention is illustrated and described in U.S. Pat. No. 3,591,348and also U.S. Pat. No. 3,471,266, issued 10/7/69 to Harold E. LaBelle,Jr. for GROWTH OF INORGANIC FILA- MENTS. The susceptor 6 is mountedwithin the furnace by attaching it to the upper end of a support rod 24that is mounted in the furnace. Rod 24 may be mounted to the base 2 ofthe furnace shown in U.S. Pat. No. 3,471,266.

Production of a solid eutectic body is initiated by using a seed of anydesired cross-sectional configuration. Thus the seed may be a roundfilament, a flat ribbon or a crystalline body of other suitable shape.The seed crystal serves as a nucleating medium for the melt and may alsobe used to establish a film of melt in the upper surface 20 of the dieassembly. The seed may be a single crystal of one of the components ofthe eutectic composition or may be a previously solidified body ofsubstantially the same composition as the melt. The essentialrequirement of the seed is that it be wetted by the melt.

The method of the present invention will now be described with referenceto the apparatus of FIG. 1. Assume for ease of description that thecrucible 2 and the susceptor 6 are mounted in an induction furance ofthe type described in U.S. Pat. No. 3,471,266, with the crucible and thecapillaries of the die assembly filled with a melt of a selected binaryeutectic composition and an inert gas atmosphere being continuouslycirculated through the furnace. Assume also that a seed 26 in the formof a monocrystal of one of the constituents of the eutectic or a singlecrystal of the eutectic composition is supported by the crystal pullingmechanism associated with the furnace in coaxial alignment with rod 18.With the upper surface 20 of rod 18 at a temperature of about -40Chigher than the eutectic point temperature of the melt composition inthe crucible, the seed is lowered into contact with surface 20 and heldthere long enough for its end to melt and form a liquid film 32 thatconnects with the melt in the capillaries 22 (see FIG. 2). It is to benoted that the capillaries are shown empty in FlGS. l-2 in order torender them more distinct to the reader and that before the end of theseed is melted to form film 32 the melt in each capillary has a concavemeniscus with the edge of the meniscus being substantially flush withthe surface 20. It is to be noted also that the temperature gradientalong the length of the seed is one factor influencing how much of theseed melts and forms film 32. The seed 26 functions as a heat sink sothat its temperature is lower at successively higher points therein.However, the thermal gradients along the seed and vertically across thefilm 32 are affected by the power input to the induction heating coil ofthe furnace and the height and distance of the heating coil andsusceptor 6 relative to the seed and the die assembly. In practice theseparameters are adjusted so that the film 32 is maintained at a thicknessin the order of 0.2 mm during growth of desired eutectic solid. Afterthe film 32 has connected with the melt in the capillaries, the pullingmechanism is actuated so as to pull the seed vertically away from thesurface 20. The initial pulling speed is set so that surface tensionwill cause the film 32 to adhere to the seed long enough forsolidification to occur due to a drop in temperature at the seed-liquidfilm interface. This drop in temperature occurs because of movement ofthe seed away from surface 20, i.e., because the solid-liquid interfaceadvances vertically to a relatively cooler region. It is to be notedthat radiative and conductive heat losses from the seed cause it toexhibit a decrease in temperature with an increase in distance from thesurface 20. If it is desired that the eutectic solid have a constantcross-section conforming in shape and area to surface 20, it isnecessary to have the film 32 fully cover surface 20. Accordingly, ifthe film initially established by melting the seed does not fully coversurface 20, the pulling speed must be set so that surface tension willcause the film to spread radially out to the edge of surface 20 assolidification progresses.

Preferably enough of the seed is melted for the film 32 to fully coverthe end surface of the die assembly, in which case the initial pullingspeed is set at the level at which solidification will occur on the seedacross the full expanse of the film. If the initial film covers lessthan all of the surface 20, a pulling speed is used at the beginning ofthe solidification process which will cause the film to spread radially,and once the surface 20 is fully covered, the pulling speed is increasedto a level at which the film is maintained at a suitable thickness andsolidification will occur on the seed along the full expanse of thefilm. It is to be noted that the pulling speed and the temperature ofthe film control the film thickness which also controls the rate of filmspreading. Increasing the temperature of surface 20 (and hence theaverage temperature of film 32) and increasing the pulling speed (butshort of the speed at which the seed and the growth occurring thereonwill pull clear of the film) each have the effect of increasing the filmthickness.

As the seed is pulled away from surface 20, liquid from film 32 willsolidify on the seed at all points along the full horizontal expanse ofthe film, with the result that additional accretions of solid will forma longer and longer solid eutectic body. The liquid consumed bysolidification at the interface of the growing solid and the film 32 isreplaced by additional melt which is supplied to surface 20 viacapillaries 22 under the influence of surface tension. The rate at whichfresh melt is supplied to the surface 20 is determined by the number andsize of the capillaries and, within limits, is always enough to maintainthe film 32. The process may be continued until the solid extension onthe seed has grown to a desired length or until the supply of melt inthe crucible has been depleted to the point where the bottom end of thecapillaries are no longer trapped, whichever event occurs first.Furthermore, the growth process may be terminated at any time byincreasing the pulling speed enough to cause the growing body to pullfree of the melt film. Once growth has been terminated, the furnace isshut down and the seed with its newly acquired eutectic extension isremoved for inspection and use.

Because of the sharp temperature gradient that is attainable across themelt film and because the average temperature of the melt film can bemaintained constant at a level near to but below the temperature of themelt in the crucible, it is possible to achieve a constant thermalgradient in the film below the solid-liquid interface and to maintain aplanar solid-liquid interface, with the result that by preferablyadjusting the pulling speed and hence the solidification rate, it ispossible to achieve a predetermined and uniform micromorphology. This isparticularly important for eutectics that have been shown to exhibit atendency to undergo a change in morphology, e.g. a transition fromrod-like to lamella structure, or a change in inter-rod or interlamellaspacing, with increasing growth rate. Furthermore, since the filmthickness is relatively small and the film is remote from the crucible,the solidification process is relatively free of perturbations of thetype that produce localized depletions of one phase in the other. Suchareas of localized phase depletions are known to be sources of prematurefailure under stress.

FIG. 3 relates to a preferred modification of apparatus used inpracticing the invention. In this case the die assembly 14A consists ofthe disc 16 and a rod 18A which is secured within a centrally locatedhole in the disc. Like rod 18, rod 18A extends a short distance abovethe disc. The bottom end of rod 18A extends close to and may even engagethe bottom of the crucible. Rod 18A has a flat substantially horizontaltop surface 20 which functions to support a film of melt 32. However,rod 18A differs from rod 18 in that it is a po rous member characterizedby a myriad of small interconnected open cells sized to function ascapillaries whereby melt will rise in the rod by capillary action.Preferably the cells are sized so that melt will rise to the top surface20 by capillary action so long as the level of the melt in the crucibleis high enough to trap the bottom end of the rod. As with rod 18, rod18A is made of a material that is wetted by the melt but will not reactwith the melt or the crucible at the operating temperatures.

Growth of eutectic bodies with the apparatus of FIG. 3 is accomplishedin the same manner as with the apparatus of FIGS. 1 and 2, except that(l the melt rises in rod 18A via the open interconnected cells ratherthan through discrete bores as shown at 22, and (2) because thecapillary action occurs across the full cross-section of rod 18A,infeeding of melt to the film 32 involves little or no horizontal flowof melt along surface 20 as may occur with rod 18. This substantialelimination of flow of fresh melt laterally along surface 20 minimizesperturbations. Furthermore, with the film being replenished with freshmelt at a large number of points instead of at a limited number ofpoints as is the case when using capillary bores 22, it is easier tomaintain an even melt thickness.

it is recognized that the choice of seed, crucible, susceptor and dieassembly materials and the determination of satisfactory operatingtemperatures and pulling speeds will vary in accordance with theeutectic to be solidified, and also that such choice is well within theskill of the art. Accordingly, the following specific examples, whichare provided to assure a full and accurate understanding of theinvention, should be considered to merely illustrate and not to limitthe invention.

EXAMPLE I A crucible having the general appearance of the crucible 2ofFlG. 2 and made of nickel is mounted on rods 8 in a susceptor 6 thatis mounted in a furnace in the manner shown in HO. 1 of US. Pat. No.3,471,266.

- The rod 8 is made of alumina and the susceptor 6 is made ofmolybdenum. Disposed in the crucible is a die assembly constructedgenerally as shown in FIG. 1. The

rod 18 is made of nickel and has four capillaries 22 of about 0.040 inchdiameter spaced uniformly about its center axis. The crucible has aninternal diameter of about 1 inch and an internal depth of about 1.5inches. The rod 18 has an outside diameter of about Va inch and a rodlength such that its upper end projects about 1/16 inch above thecrucible. The crucible is filled with a solid composition comprising 23%UP and 77% NaCl by weight. An elongate seed crystal 26 consisting of UPis mounted in the seed holder of the crystal pulling mechanismassociated with the furnace so that it is aligned with rod 18. The seedcrystal is supported in axial alignment with rod 18.

With the crucible mounted in the furnace, the induction heating coil ofthe furnace is located so that its upper end is approximately even withthe middle of the susceptor and its lower end at least even andpreferably a little below the susceptor. Then the furnace enclosure isevacuated and filled with argon gas to a pressure of about oneatmosphere which is maintained during the growth period, and theinduction heating coil is energized and operated so that the charge inthe crucible is brought to a fully molten condition and the surface 20is brought to a temperature of about 700C. As the charge in the crucibleis converted to the melt 4. columns of melt will rise in and till thecapillaries 22. Each column of melt rises until its meniscus issubstantially flush with the top surface 20 of rod 18. After affordingtime for temperature equilibrium to be established, the pullingmechanism is activated and operated so that the seed 26 is moved downinto contact with the upper surface 20 and allowed to rest in thatposition long enough (e.g. about one minute) for the bottom end of theseed to melt and form a film 32 which fully covers surface 20 andconnects with the melt in the capillaries. Then the seed is withdrawnvertically at a rate of about 0.1 inch per minute. As the seed iswithdrawn, surface tension causes film material to adhere to the seedand also cause additional melt to flow out of the capillaries and add tothe total volume of film. The liquid film material adhering to the seedexperiences a temperature drop due to its movement away from therelatively hotter surface 20 and the fact that the seed functions as aheat sink. As a consequence of this temperature drop, the liquid that isin contact with the seed undergoes directional solidification and growthof solid occurs on the seed. Concurrently with the consumption of filmby growth of solid on the seed, surface tension causes additional meltto flow up out of the capillaries onto surface 20 to replenish the film.The pulling speed and temperature are maintained constant and growth ofsolid on the seed continues to propagate vertically throughout theentire horizontal expanse of the film 32, with the result thatsuccessive accretions of solid form an elongate extension on the seedhaving substantially the cross-sectional shape and area of surface 20(the openings of capillary 20 may be disregarded in considering what isthe configuration of surface 20 since they are filled with melt). Growthis continued until the growth on the seed has reached a length about6inches. Thereafter the pulling speed is increased rapidly to about 10inches per minute, with the result that the grown body pulls free of thefilm 22. Then the furnace is cooled and the seed retrieved forsectioning and ex amination of the grown body.

FlG. 5 is a photomicrograph of a transverse microspecimen, magnified bya factor of 940, of a eutectic body produced by practicing the inventionaccording to the procedure of the foregoing example. The eutectic bodywas found to be of uniform morphology throughout its entire volume. Asis apparent from FIG. 5, the eutectic body consists of substantiallyuniformly sized rods spaced substantially uniformly throughout a matrixphase. The rod diameters are in the order of 0.0001 inches and thespacing between rods is in the order of 0.00015 inches. The rods extendparallel to the direction of solidification. The rods have been found tobe of indefinite length, with the result that the body is characterizedby a high aspect ratio, (i.e., the ratio of rod length to rod diameter).

EXAMPLE I] A eutectic body consisting of 56% UP and 44% CaF is producedby using the same apparatus and following the same procedures as inExample I, except that the crucible is initially charged with UP and CaFin the above proportions, the furnace is operated so as to hold the topsurface 20 of the die assembly at a temperature of about 775C, and thepulling speed of the crystal is maintained at about 0.1 inch per minute.

FIG. 6 is a photomicrograph similar to FIG. 5 ofa microspecimen,magnified by a factor of 940, of a LiF-CaF eutectic body produced inaccordance with the procedure of Example II. As is evident, the productis a lamellar or plate-type eutectic, the LiF phase being in the form ofplates of indefinite length dispersed through a CaF matrix. As with theLiF-NaCl eutectic, it has a coherent microstructure, the two phaseshaving an exceptionally high degree of regularity with the parallelalternate lamellae extending parallel to the direction ofsolidification.

EXAMPLE III A crucible having the general appearance of the crucible 2of FIG. 2 and made of alumina is mounted on rods 8 in a susceptor 6 thatis mounted in a furnace of the type shown in FIG. 1 of U.S. Pat. No.3,471,266, except that the pulling mechanism is constructed inaccordance with the teachings of U.S. Pat. No. 3,552,931, issued Jan. 5,1971 to Paul R. Doherty et al., for APPARATUS FOR IMPARTING TRANSLA-TIONAL AND ROTATIONAL MOTION, so that the seed crystal (and the growththat occurs thereon) will undergo rotational motion as it is beingwithdrawn. The rods 8 are made of alumina and the susceptor 6 is made ofmolybdenum. Disposed in the crucible is a die assembly constructed asshown in FIG. 2A and made of an alumina foam or sponge which consists ofa myriad of small interconnected open cells having an average diameterin the order of 0.0002 inch. The diameter and length of rod 18A and thedepth and internal diameter of the crucible are the same as specified inExample I. Into the crucible is placed an aluminum-nickel ingotcomprising 6.2 weight per cent nickel. The ingot is prepared byinductively melting substantially pure aluminum and nickel in an argonatmosphere at 900C for 1 hour to assure complete mixing, and thencooling the melt. An elongate aluminum seed crystal is mounted in theseed holder of the crystal pulling mechanism associated with thefurnace. Then with the induction heating coil located as described inExample I, the furnace enclosure is evacuated and filled with argon to apressure of about one atmosphere and the heating coil is energized. Thefurnace temperature is raised high enough to melt the ingot and thenadjusted so as to hold the temperature of the upper surface of rod 18Aat about 675C. The molten liquid in the crucible infiltrates the cellsof rod 18A and rises up to its top surface by action of capillary rise.After the cells of rod 18A are filled with melt, the crystal pullingmechanism is operated to move the aluminum seed down into contact withthe upper surface of rod 18A and held there long enough for its bottomend to melt and form a thin film that extends along surface 20. Then thepulling mechanism is operated to withdraw the seed vertically at a rateof about 2 centimeters per hour while the temperature of surface 20A isheld steady at about 675C. As the seed is withdrawn, liquid filmmaterial solidifies on the seed and surface tension causes additionalmelt to flow up rod 18A to the film on surface 20A to replace thematerial lost by solidification. About 10 minutes after solidificationis evident on the seed, the pulling mechanism is caused to rotate theseed at a rate of about 10 degrees per hour at the same time that it isbeing pulled. The pulling and rotational speeds are held constant andgrowth of solid continues to propagate vertically on the seed to across-sectional configuration corresponding to the shape of surface 20.Growth is terminated when the supply of melt in the crucible issubstantially exhausted. Thereafter the furnace is cooled and the seedretrieved from the pulling mechanism for sectioning and examination ofthe grown body. An Al-Al Ni body grown according to this example has aeutectic microstructure consisting of a lamellar micromorphology. Thebody has substantially parallel alternating lamellae of each phase withall of the lamellae extending spirally about the bodys longitudinalaxis. The lamellae are coextensive and substantially free ofdiscontinuities. It also is possible to produce a rod-like eutecticmicrostructure, i.e., a micromorphology consisting of thin parallel rodsof Al Ni embedded in a continuous matrix of Al, by increasing thepulling speed (and hence the solidification rate) to about 8-10centimeters per hour. If the seed is rotated at an appropriate speed,the parallel rods of Al Ni will also extend spirally about the growthaxis. If the seed is not rotated, the lamellae and rods will extendparallel to the growth axis.

Other eutectic alloys also may be grown with a twisted structure using apulling procedure like that of Example III. It also is possible bysolidification of the film-supporting surface of the die, e. g. byproviding one or more blind holes or cavities 38 as shown in FIG. 4 thatare too large in diameter to function as a capillary, to grow eutecticbodies having one or more through holes extending parallel to the axisof growth. In this case it is preferred to use a seed crystal in theform of a hollow tube 40 as shown or a solid body that has a crosssection with a substantially smaller area than the upper surface 20 ofthe rod of the die assembly 14B. In the latter case the initial filmthat is formed may cover less than all of the surface 20 and must bemade to spread out around the cavity 38 so as to fully cover the surface20; hence the initial growth of solid will not conform to the desiredshape but will grow to that shape as the film spreads out over surface20.

It also is to be understood that the eutectic compositions may includetrace amounts of impurities or minor amounts of selected elementsintroduced for reasons obvious to persons skilled in the art withoutdeparting from the present invention. Accordingly, the term essentiallyconsisting of as used herein with respect to the eutectic composition isintended to allow for such additional impurities or selected elements.

Eutectic bodies produced according to this invention offer a number ofadvantages. The most important advantage is a high degree of regularityof the phases with the phases being substantially free ofdiscontinuities. Thus, for example, in a eutectic body having a rod-likemorphology, the individual rods will extend for substantially the fulllength of the body. The ability to produce a body with one or more holesavoids the problem of irregular phase termination and particle breakoutsuch as occurs when a hole is drilled in an alloy body. Growing a bodyso that the phases are curved about the bodys longitudinal axis isadvantageous when it is desired to machine a curved part. By properlycontrolling the speed at which the body is rotated as it is being grown,it is possible to have the phases oriented so that machining transverseto the direction of the phases can be avoided when the body is beingmachined into a finished part of predetermined size and shape.Furthermore, since the pulling rate is consistent with the rate ofgrowth along the pulling axis (which in turn depends upon thetemperature gradient across the film from which growth occurs), it ispossible by controlling the rate of heat input and the rate of heat lossby radiation and conduction to control the rate of growth within closelimits and to maintain the film thickness substantially constant. Alsosince the film is supported by the end surface of the die and itsposition with respect to the height of the heater coil is held fixed,the solidliquid interface is substantially planar at all times while aeutectic body is being grown. Another important advantage is that it ispossible to grow eutectic bodies with any one of a variety of arbitrarycross-sectional configurations, e.g., a body having the generalcrosssectional shape of an air-foil with one or more holes extendinglengthwise of the body. Still other advantages, in addition to thosenoted above, will be obvious to persons skilled in the art.

What is claimed is:

1. Method of producing polyphase eutectic bodies of uniform morphologycomprising:

establishing a thin liquid film of a eutectic composition on asubstantially flat supporting surface and controlling the temperature ofsaid film so that it has (1) a sharp temperature gradient along itsdepth with the film being hottest at said surface, (2) a substantiallyflat temperature profile along its length and breadth, and (3) anaverage temperature approximately equal to the eutectic pointtemperature of said composition; solidifying and pulling a mass of saidcomposition from the cooler side of said film at a selected rate; andsimultaneously supplying an additional quantity of said mixture inliquid form to said surface to replace the liquid consumed in producingsaid eutectic mass. 2. Method according to claim 1 wherein said eutecticcomposition is a binary composition.

3. Method according to claim 1 wherein said eutectic composition is analloy.

4. Method according to claim 3 wherein said alloy essentially comprisesnickel and aluminum.

5. Method according to claim 4 wherein said alloy essentially comprisesnickel, indium and antimony.

6. Method according to claim 1 wherein said mass is turned about itspulling axis as it is pulled from said film.

7. Method according to claim 1 wherein said flat supporting surface isporous.

8. Method according to claim 7 wherein said porous surface is part of amember consisting of a myriad of interconnected open cells, and furtherwherein said additional quantity of said mixture is supplied to saidsurface via said cells.

9. Method of producing a polyphase eutectic body having a coherentmicrostructure comprising:

establishing a thin liquid film of a selected eutecticcomposition on asubstantially horizontal and planar end surface of a heat conductingmember, and controlling the temperature of said film so that it has (1)a sharp vertical temperature gradient, (2) a substantially flathorizontal temperature profile, and (3) an average temperatureapproximately equal to the eutectic point temperature of saidcomposition;

growing and vertically withdrawing a coherent polyphase solid body fromsaid film at a selected rate; and

supplying additional quantities of said composition in liquid form tosaid end surface via a passageway in said member as said solid body isbeing grown to replace the liquid consumed in producing said body.

10. Method according to claim 9 wherein the thickness of said film isheld substantially constant during growth and withdrawal of said body.

11. Method according to claim 9 wherein growth of said body is initiatedby use of a crystalline seed.

12. Method according to claim 9 further including the step of rotatingsaid body as it is withdrawn from said film.

13. Method according to claim 9 wherein said member is supported in aheated crucible containing a reservoir supply of said selectedcomposition in liquid form,

and said film is replenished from said reservoir supply.

2. Method according to claim 1 wherein said eutectic composition is abinary composition.
 3. Method according to claim 1 wherein said eutecticcomposition is an alloy.
 4. Method according to claim 3 wherein saidalloy essentially comprises nickel and aluminum.
 5. Method according toclaim 4 wherein said alloy essentially comprises nickel, indium andantimony.
 6. Method according to claim 1 wherein said mass is turnedabout its pulling axis as it is pulled from said film.
 7. Methodaccording to claim 1 wherein said flat supporting surface is porous. 8.Method according to claim 7 wherein said porous surface is part of amember consisting of a myriad of interconnected open cells, and furtherwherein said additional quantity of said mixture is supplied to saidsurface via said cells.
 9. Method of producing a polyphase eutectic bodyhaving a coherent microstructure comprising: establishing a thin liquidfilm of a selected eutecticcomposition on a substantially horizontAl andplanar end surface of a heat conducting member, and controlling thetemperature of said film so that it has (1) a sharp vertical temperaturegradient, (2) a substantially flat horizontal temperature profile, and(3) an average temperature approximately equal to the eutectic pointtemperature of said composition; growing and vertically withdrawing acoherent polyphase solid body from said film at a selected rate; andsupplying additional quantities of said composition in liquid form tosaid end surface via a passageway in said member as said solid body isbeing grown to replace the liquid consumed in producing said body. 10.Method according to claim 9 wherein the thickness of said film is heldsubstantially constant during growth and withdrawal of said body. 11.Method according to claim 9 wherein growth of said body is initiated byuse of a crystalline seed.
 12. Method according to claim 9 furtherincluding the step of rotating said body as it is withdrawn from saidfilm.
 13. Method according to claim 9 wherein said member is supportedin a heated crucible containing a reservoir supply of said selectedcomposition in liquid form, and said film is replenished from saidreservoir supply.